Alternating current (AC) electric motors are considered constant-speed devices, but their speeds can be varied by changing the input voltages or frequencies or by changing the windings that make the electric motors rotate. The most common way of changing the speed of an AC electric motor is to vary the input frequency using an inverter as the power supply, which has become more popular with the increased development and decreased cost of power electronics. Another way of changing the speed involves reducing the voltage to the motor windings using resistors, transformers, or motor winding taps, which is preferred for certain applications.
In particular, an AC electric motor may be provided with a particular number of taps on its main winding, and these taps allow the electric motor to run with different voltages applied to its magnetic field. Typically, the number of taps and the number of speeds available for a particular electric motor is not more than four. A common application of this method involves fans that have low, medium, and high speeds which are selectable with simple switches. For this and similar applications, it is generally not necessary to achieve exact motor speeds, and it is desirable to keep costs relatively low.
Tap-based motor interfaces have either direct tap inputs or multiplexed tap inputs which base outputs on tap input patterns at multiple input channels. If a different tap input pattern is desired, the firmware must be reprogrammed with a different tap input logic, which causes delays and increased costs. Further, the number of valid taps is fixed by the hardware and the software.
This background discussion is intended to provide information related to the present invention which is not necessarily prior art.